MLA

Van Vechten, Carl, 1880-1964. Matisse, Pierre. Box 366, folder 5133. 1933 May 20. https://collections.library.yale.edu/catalog/2066672.

APA, 6th edition

Van Vechten, Carl, 1880-1964. (["Box 366, folder 5133"])(1933 May 20)[Matisse, Pierre]. https://collections.library.yale.edu/catalog/2066672.